Geographic Origin and Life History Characteristics Predict the Responses of Plants to Reintroduction of a Native Herbivore
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Authors
Acuña, Kierstin M.
Issue Date
2024
Type
Thesis
Language
Keywords
Biotic Resistance , Environmental/temporal Heterogeneity , Invasive Exotic Species , Plant Community Ecology , Plant Functional Groups , Reintroduced Large Mammalian Herbivores
Alternative Title
Abstract
In response to the decline of large mammals in many parts of the world, a wealth of programs have been initiated over the past century to reintroduce extirpated taxa into parts of their historical range. Although these reintroductions have been a resounding success in many cases, and extensive research has been conducted to understand the dynamics of reintroduced populations, remarkably little attention has been focused on how the return of long-absent mammals – especially herbivores – has affected plant communities in recipient ecosystems. The response of plant communities to reintroduced herbivores will likely be complex, given that reintroduction sites have often been invaded by many non-native plant species and these taxa and their native counterparts vary greatly in life history characteristics and life forms. Here, we summarize results from a 25-year-old exclosure experiment stratified across three grassland types to examine the effects of reintroduced tule elk ( Cervus canadensis nannodes ) on a coastal plant community in northern California. Our results indicate that elk increased the dominance, species richness, and relative cover of exotic plant species, with the most abundant group in our system – exotic annual graminoids – increasing cover by 25%. We also found that elk had mixed effects on native species, with no effects on native graminoids and negative effects on native forbs and shrubs. The latter finding indicates that elk slowed the progression of woody encroachment in this system. Offering support for the biotic resistance hypothesis, we found that the prevalence of exotic species in our system decreased with increasing native richness, and elk dampened this relationship. Finally, we often found that the effects of elk on the plant community were context dependent, varying both spatially and temporally. In conclusion, our results highlight an important but sobering reality – conservation efforts that reintroduce formerly extirpated mammals to parts of their former range will often have a complex array of desirable and undesirable effects on recipient plant communities.